Respiratory tract infections are caused by a variety of microorganisms. Infections which are persistent have a myriad of consequences for the health care community including increased treatment burden and cost, and for the patient in terms of more invasive treatment paradigms and potential for serious illness or even death. It would be beneficial if an improved treatment paradigm were available to provide prophylactic treatment to prevent susceptible patients from acquiring respiratory tract infections as well as increasing the rate or effectiveness of eradicating the infections in patients already infected with the microorganisms.
In particular, cystic fibrosis (CF) is one example of a disease in which patients often acquire persistent or tenacious respiratory tract infections. CF is a life-threatening genetic disease affecting approximately 30,000 people in the United States with a frequency of approximately one in every 2,500 live births (Fitzsimmons S C, 1993). The name cystic fibrosis refers to the characteristic scarring (fibrosis) and cyst formation within the pancreas, first recognized in the 1930s. About 1,000 new cases of CF are diagnosed each year. More than 80 percent of patients are diagnosed by age three; however, nearly 10 percent of newly diagnosed cases are age 18 or older.
The primary CF defect is expressed as altered ion transport via the cystic fibrosis transmembrane conductance regulator (CFTR), which is the protein regulating cyclic-AMP-mediated chloride conductance at the apical membranes of secretory epithelia (Schroeder S A et al., 1995). Specifically, the normal release of intracellular chloride into extracellular fluids fails to respond to normal cAMP elevation. This impaired release of chloride results in the dehydration of surrounding respiratory and intestinal mucosal linings and impaired sodium reabsorption of the sudoriferous glands. This mucosal dehydration, coupled with inflammatory and infective by-products, creates a thick and tenacious mucus that clogs and damages airways. Prompt, aggressive treatment of CF symptoms can extend the lives of those with the disease.
Although most people without CF have two working copies of the CFTR gene, only one is needed to prevent cystic fibrosis. CF develops when neither gene works normally. Therefore, CF is considered an autosomal recessive disease. There are more than 1,500 different genetic mutations associated with the disease (CFTR mutation database, 2006), thus making homozygous and heterozygous screening procedures difficult (Zielenski J et al., 1995). However, approximately two thirds of the mutations are found to be delta F508, making it the most common CF mutation (CF Genetic Analysis Consortium, 1994).
The ongoing treatment of CF depends upon the stage of the disease and the organs involved. Clearing mucus from the lungs is an important part of the daily CF treatment regimen. Chest physical therapy is one form of airway clearance, and it requires vigorous percussion (by using cupped hands) on the back and chest to dislodge the thick mucus from the lungs. Other forms of airway clearance can be done with the help of mechanical devices used to stimulate mucus clearance. Other types of treatments include: Pulmozyme®, an inhaled mucolytic agent shown to reduce the number of lung infections and improve lung function (Hodson M, 1995); TOBI® (tobramycin solution for inhalation), an aerosolized aminoglycoside antibiotic used to treat lung infections and also shown to improve lung function (Weber A et al., 1994); and oral azithromycin, a macrolide antibiotic shown to reduce the number of respiratory exacerbations and the rate of decline of lung function (Wolter J et al., 2002).
As discussed above, high rates of colonization and the challenge of managing Pseudomonas aeruginosa infections in patients with cystic fibrosis (CF) have necessitated a search for safe and effective antibiotics. Currently, therapy with an aminoglycoside in combination with a beta-lactam or a quinolone antibiotic is the standard. A 96-week series of clinical studies including 520 patients with moderate-to-severe CF showed that patients receiving inhaled tobramycin spent 25 to 33% fewer days in the hospital and experienced significant increases in lung function (Moss R B, 2001). These results demonstrate the effectiveness of inhaled antibiotics to treat CF. However, the development of drug resistant strains, especially P. aeruginosa, is a major concern with the long-term delivery of aerosolized antibiotics via inhalation (LiPuma J J, 2001).
While azithromycin possesses activity against Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pneumoniae, it has no direct activity against Pseudomonas aeruginosa, Burkholderia cepacia, or other gram-negative non-fermenters (Lode H et al., 1996). Tobramycin possesses activity against P. aeruginosa; however, the increase in the number of patients with resistant isolates on continuous therapy from ˜10% to 80% after 3 months (Smith A L et al., 1989) has led to the intermittent dosing regimen of 28-days-on followed by 28-days-off therapy. Even on intermittent inhaled tobramycin therapy, the percentage of patients with multiresistant P. aeruginosa increased from 14% at baseline to 23% after 18 months of treatment (LiPuma J J, 2001). The development of a therapeutic regimen that delivers the anti-infective therapy in a continuous fashion, while still inhibiting the emergence of resistant isolates, may provide an improved treatment paradigm. It is noteworthy that chronic P. aeruginosa airway infections remain the primary cause of morbidity and mortality in CF patients. When patients experience pulmonary exacerbations, the use of antipseudomonal therapy, frequently consisting of a β-lactam and an aminoglycoside, may result in clinical improvement and a decrease in bacterial burden. Eradication of the infection, however, is quite rare.
In CF airways, P. aeruginosa initially has a non-mucoid phenotype, but ultimately produces mucoid exopolysaccharide and organizes into a biofilm, which indicates the airway infection has progressed from acute to chronic. Bacteria in biofilms are very slow growing due to an anaerobic environment and are inherently resistant to antimicrobial agents, since sessile cells are much less susceptible than cells growing planktonically. It has been reported that biofilm cells are at least 500 times more resistant to antibacterial agents (Costerton J W et al., 1995). Thus, the transition to the mucoid phenotype and production of a biofilm contribute to the persistence of P. aeruginosa in CF patients with chronic infection by protecting the bacteria from host defenses and interfering with the delivery of antibiotics to the bacterial cell.
Although much effort has been made to improve the care and treatment of individuals with CF, and the average lifespan has increased, the median age of survival for people with CF is only to the late 30s (CF Foundation web site, 2006). Thus, a continuing need exists for improved formulations of anti-infectives, especially for administration by inhalation. The present invention addresses this need.
Ciprofloxacin is a fluoroquinolone antibiotic that is indicated for the treatment of lower respiratory tract infections due to P. aeruginosa, which is common in patients with cystic fibrosis. Ciprofloxacin is broad spectrum and, in addition to P. aeruginosa, is active against several other types of gram-negative and gram-positive bacteria. It acts by inhibition of topoisomerase II (DNA gyrase) and topoisomerase IV, which are enzymes required for bacterial replication, transcription, repair, and recombination. This mechanism of action is different from that for penicillins, cephalosporins, aminoglycosides, macrolides, and tetracyclines, and therefore bacteria resistant to these classes of drugs may be susceptible to ciprofloxacin. Thus, CF patients who have developed resistance to the aminoglycoside tobramycin (TOBI), can likely still be treated with ciprofloxacin. There is no known cross-resistance between ciprofloxacin and other classes of antimicrobials.
Despite its attractive antimicrobial properties, ciprofloxacin does produce bothersome side effects, such as GI intolerance (vomiting, diarrhea, abdominal discomfort), as well as dizziness, insomnia, irritability and increased levels of anxiety. There is a clear need for improved treatment regimes that can be used chronically, without resulting in these debilitating side effects.
Delivering ciprofloxacin as an inhaled aerosol has the potential to address these concerns by compartmentalizing the delivery and action of the drug in the respiratory tract, which is the primary site of infection.
Currently there is no aerosolized form of ciprofloxacin with regulatory approval for human use, capable of targeting antibiotic delivery direct to the area of primary infection. In part this is because the poor solubility and bitterness of the drug have inhibited development of a formulation suitable for inhalation. Furthermore, the tissue distribution of ciprofloxacin is so rapid that the drug residence time in the lung is too short to provide additional therapeutic benefit over drug administered by oral or IV routes.
Phospholipid vehicles as drug delivery systems were rediscovered as “liposomes” in 1965 (Bangham et al., 1965). The therapeutic properties of many active pharmaceutical ingredients (APIs) can be improved by incorporation into liposomal drug delivery systems. The general term liposome covers a wide variety of structures, but generally all are composed of one or more lipid bilayers enclosing an aqueous space in which drugs can be encapsulated. The liposomes applied in this program are known in the drug delivery field as large unilamellar vesicles (LUV), which are the preferred liposomal structures for IV drug administration.
Liposome encapsulation improves biopharmaceutical characteristics through a number of mechanisms including altered drug pharmacokinetics and biodistribution, sustained drug release from the carrier, enhanced delivery to disease sites, and protection of the active drug species from degradation. Liposome formulations of the anticancer agents doxorubicin (Myocet®/Evacet®, Doxyl®/Caelyx®), daunorubicin (DaunoXome®) the anti-fungal agent amphotericin B (Abelcet®, AmBisome®, Amphotec®) and a benzoporphyrin (Visudyne®) are examples of successful products introduced into the U.S., European and Japanese markets over the last decade. Furthermore, a number of second-generation products have been in late-stage clinical trials, including Inex's vincristine sulphate liposomes injection (VSLI). The proven safety and efficacy of lipid-based carriers make them attractive candidates for the formulation of pharmaceuticals.
Therefore, in comparison to the current ciprofloxacin formulations, a liposomal ciprofloxacin aerosol formulation should offer several benefits: 1) higher drug concentrations, 2) increased drug residence time via sustained release at the site of infection, 3) decreased side effects, 4) increased palatability, 5) better penetration into the bacteria, and 6) better penetration into the cells infected by bacteria. It has previously been shown that inhalation of liposome-encapsulated fluoroquinolone antibiotics may be effective in treatment of lung infections. In a mouse model of F. tularensis liposomal encapsulated fluoroquinolone antibiotics were shown to be superior to the free or unencapsulated fluoroquinolone by increasing survival (CA2,215,716, CA2,174,803, and CA2,101,241).
Another application, EP1083881B1, describes liposomes containing a drug-conjugate comprising a quinolone compound covalently attached to an amino acid. Yet another application, U.S. Publication No. 20004142026, also describes the use of liposome-encapsulated antibiotics and the potential for administration of a lower dose of a liposome-encapsulated anti-infective, by a factor of 10 or 100, than for the free unencapsulated anti-infective.
It has also been reported that the presence of sub-inhibitory concentrations of antibiotic agents within the depths of the biofilm will provide selective pressures for the development of more resistant phenotypes (Gilbert P et al., 1997). This may be partly due to the failure of the antibiotics to penetrate the glycocalyx adequately.